AS15-9309(P)

Figure 190

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Pictured here is a lunar sinuous rille located in the eastern part of Mare Serenitatis. It is interpreted to be a lava channel because it resembles terrestrial lava channels like the one in figure  189. The rille starts in a crater (presumably the volcanic source) and follows a sinuous course downhill. The channel edges are marked by low ridges resembling those that form on actively flowing lava channels on Earth; the terrestrial ridges are formed when the outer edges of the molten lava chill and make natural levees. The lower reaches of the channel may be a lava tube that formed when the upper surface of the flowing lava chilled and froze while the hotter lava in the interior continued to flow. On the other hand, this ridge at the end of the channel may be a fracture along which lava has been extruded. Similar features are called "squeeze ups" in terrestrial lava flows. A possible small lateral lava flow is visible near the end of the feature.    -H.M.